Digital systems make extensive use of high speed electrical interconnects in routing signals among processing elements or between processing elements and memory. The design of these high speed interconnects, including all of their associated components (active buffers and their associated power delivery, packaging components, printed circuit board traces, connectors, etc.) constitutes a large fraction of the effort associated with developing many digital systems, and often the limitations associated with these components significantly constrain overall system performance. In addition, as overall system performance increases, there is a corresponding scaling of bandwidth between processing elements and in processor-memory paths.
Single-ended signaling is a commonly used method of transmitting electrical signals. One wire carries a varying voltage that represents the signal, while another wire is connected to a reference voltage, usually ground. An alternative to single-ended signaling is differential signaling. In differential signaling two complementary signals are sent on two separate wires. An advantage of single-ended over differential signaling is that fewer interconnects are needed to transmit multiple signals. If there are n signals, single-ended signaling uses n interconnects, one for each signal, plus one shared interconnect for ground. Differential signaling, on the other hand, uses at least 2n wires. A disadvantage of single-ended signaling is that large power supply voltage transients may result when multiple interconnects are switched simultaneously. This phenomenon is referred to a simultaneous switching noise (SSN). Differential signaling has many advantages (e.g., reduced crosstalk sensitivity, reduced simultaneous switching noise, etc.), but uses twice the number of interconnect traces as single-ended signaling.
The use of balanced codes has been proposed, for example, for encoding of unchangeable data on a laser disk. Examples of such balanced coding schemes can be found in: D. E. Knuth, “Efficient balanced codes,” IEEE Transactions on Information Theory, vol. 32, no. 1, pp. 51-53, 1986.